Fix revlog-ng interaction with old-http. revlog.py wasn't trying to detect the version of a revlog file that doesn't exist on the filesystem (as is the case with old-http). Additionally, there was an off-by-one error in httprangereader.read (ranges in HTTP Range headers are inclusive), making it get more data than what was asked for. This made a struct.unpack complain that "unpack str size does not match format". Finally, with the two fixes above, test-static-http fails, since BaseHTTPServer doesn't understand ranges and returns too much data. Work around that by reading only the specified amount.

%% no merges expected
%% merge should fail
abort: 'b' already exists in the working dir and differs from remote
%% merge of b expected
merging for b
merging b
%%
Contents of b should be "this is file b1"
This is file b1
%% merge fails
abort: outstanding uncommitted changes
%% merge expected!
merging for b
merging b
%% merge of b should fail
abort: outstanding uncommitted changes
%% merge of b expected
merging for b
merging b